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Electroless nickel plating is tarnishing, turning black

Q. Parts are 6061, machined, then electroless nickel plated. We are getting discoloration and "black stains" regularly on a few parts from each lot, but not on all of the parts.
These parts look good when they leave our warehouse but a couple weeks later when they get through our customers' quality they are being flagged. The "black stains" can be wiped/polished away. Any idea what is causing these "black stains"?

Chloe Condon
- Harrisburg, Pennsylvania
April 28, 2022

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⇩ Closely related postings, oldest first ⇩

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1995

Q. We've run into a bit of a problem of nickel discoloration on some heatsinks.   We build Mil-Spec high reliability computers. In one case the modules has electroless nickel on copper heatsinks. The heatsink looks vaguely like a ladder and is bonded to FR-4 multilayer circuit board (printed wiring board, or PWB). Chips straddle the rungs and are bonded down with epoxy and are soldered into the PWB using RMA rosin flux and a wave solder machine.  

We installed a semi-aqueous PWB cleaning system and the heatsinks are coming out with black water spots (well, that's a bit over stated, there are water spot shaped areas ranging from clear tan to blackish). We're desperate to find out what's causing the discoloration and more importantly, how to avoid it. (Discoloration of nickel plating does not meet Mil-Spec)   The cleaning process is a batch process with 4 sumps and a drying bay. The first sump is Axarel 46, a DuPont devised, now Petroferm sold hydrocarbon mixture (aliphatic hydrocarbon with dibasic esters: isobutyl glutarate, adipate, succinate and surfactant) - temperature 120 F, ~10-20 minute immersion, immersion spray agitation The second sump is an emulsion of DI water and Axarel - temperature 140 F, 5 minute immersion, immersion spray agitation Third and fourth sumps are DI water, 140 F, 5 minute immersion in each, immersion spray agitation. Final sump is hot air, 190 F, the rack is in the bay for 6 minutes, there is a slit nozzle at the top of the bay to act as hot air knife to blow surface water off. Naturally the problem is mainly showing up on product, not test coupons.

We did reproduce a mild case of the discoloration after taking a chunk of heatsink, bonding it to a PWB, putting epoxy tape on it, fluxing it, running it through the wave solder and then cleaning it. The discoloration appears to occur in the last spots water is standing after coming out of the final rinse before drying. We also tried cleaning a section of heatsink as-received, and after bonding to a PWB. Neither had appreciable discoloration. We sent the as-received and discolored heatsink section out for ESCA analysis of both discolored and non-discolored areas.

The as-received was dirtiest- ~2% Ni at the surface, 80% C, 10% O, smattering of Cu, Pb, Sn, P. Unstained area on stained heatsink - 20% Ni, 56% C, smattering of Cu, Pb, P. Stained area on stained heatsink - 18% Ni, 61 %C, smattering of Cu, Pb, P 40 Angstroms down ESCA shows as-received - 20% Ni, 60%C, smattering of Cu, Pb, P Unstained area - 70% Ni, 20%C, 7%P Stained area - 65% Ni, 25%C, 9%P Visually at 200X the stained area has a transparent brown tint versus the silver surface elsewhere. There are iridescent spots visible over all the surface, perhaps tending to slightly larger spots in the darker areas. (Possibly residual hydrocarbon? - it does have a boiling point of 350 F)  

Anyone have thoughts as to what it is, how better to identify it, or how to prevent forming it? We got a suggestion that electroless typically would have an inhibitor applied to prevent discoloration, is this common? Would the cleaning process remove this?

Steven Axdal
- Bloomington Minnesota

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Electroless nickel tarnished with rainbow colors during heat treatment

1998

Q. I am an electroplating jobber in Penang, Malaysia. My company provide gold, silver, palladium-nickel, tin, tin-lead and electroless nickel (EN) plating to the electronic and electrical industries.

I had lately doing some EN coating jobber that require heat treatment, the job pieces tarnished with rainbow colors in the heating chamber. What caused this? Could you share some experience with me?

After the EN coating we passivate the surface with dilute chromic acid. Then heated in nitrogen gas purging oven with the following profile:

Thank you and best regards,

Keat-Seng Ong
- Malaysia

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Q. I'm putting an electroless nickel finish (approx. .0004" thick) on a machined Aluminum (6061-T6) part that is then glass bead blasted (240 grit) prior to plating. The matte finish is very attractive and consistent but highly vulnerable to tarnishing from handling (hand/finger sweat). Is there any way to alleviate this problem? What is the most effective cleaner to remove the tarnish (preferable a cloth type)?

Thank you,

Duncan Mackay
- Palo Alto, California, USA
2003

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Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)

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Q. Is it possible to Alodine an electroless nickel plated part (aluminum base metal)? I'm assuming the Alodine finish would lessen finger printing of the nickel and would make these unsightly marks easy to remove, probably with a damp cloth? If this is all feasible then how long should the part be submerged in the chromate solution for the best result?

Thank you.

Duncan Mackay
- Palo Alto, California, USA
2003

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2004

Q. Electroless Nickel Plating on Aluminium turns black with Phosphate buffer. We tested Nickel plated aluminium with Phosphate Buffer After one day nickel plating turns dark brown/ black, which cannot be removed by water. Nickel coating is around 10 um, phosphor content 8 to 10 %

Questions: ( I am mechanical engineer, not a chemist)
- is this corrosion?
- can we clean off the black deposition? with what?
- what can we do to make the coating to resist phosphate buffer (and still be electrically conductive)
- thicker coating?
-other nickel content?
- any other thin coating for aluminium, which is conductive and resists phosphate buffer?
- anything else?

Any info appreciated

Stephan Sattler
Medical Instruments design - Starnberg, Bavaria, Germany

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2005

Sir,

We own a plating shop of Electroless Nickel plating process. We use SS 304 tank with bottom heater to heat the plating bath. At the end of 2.5 turnover of the bath life we get black colouration on components if we plate in it. But if we try with same bath solution in a glass beaker [beakers on eBay or Amazon] /plastic vat we don't get black colour on components that are plated. We passivated the tank(SS) and we even filtered the solution with activated carbon and tried plating in SS tank. But still the problem persists. We used a new plating solution in the same tank . We find no black colouration of components occurs.

Please give us a correct solution.

Nirupama Balasubramanian
- Chennai, Tamilnadu, India

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Q. We have been using an electroless nickel plated (0.2 mils) aluminum electrical connector for a number of years on a power supply. Our supplier solders wires to it, uses some RTV to hold some of the wires, fills the Tin plated, cold rolled steel box with a heat-activated epoxy and alumina, mechanically attaches the connector to the box, without sealing around it, and heats the box to 80 °C for 4-6 hours. After a few years we are noticing a black "tarnish" that seems to have "creeped" up the walls of the inside of the connector - not all the way. We also see some "white" deposits at the bottom of the connector. We are seeing: Ni, Zn, S, K, Ti, Al in these areas; none of these elements are in the epoxies. Also of note, the customer exposed the power supply to 130C coolant while not operating for two hours. Does anyone have an idea what could be happening? Our customer is concerned about long term corrosion and products of conducting material falling off.

Geoffrey M Smith
Power Supply Design Engineer - Baltimore, Maryland, USA
2007

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Q. My company plates a variety of materials with mid-phos electroless nickel. Recently, we have seen some discoloration form as the plated material ages in the form of a black tarnish that retains some of the shine on our copper alloy parts. The parts are rinsed in hot DI water post plate, as all our nickel plated parts are, and none of the other plated parts have shown this malady. Other than surface contamination and reaction in post plating processes, what would cause this to occur (what type of contamination)?

Allen Clague
Plating manager - Waynesboro, Virginia
2007

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Tarnish of electroless nickel over brass or alum. when ultrasonic aqueous cleaning

We have thousands of parts Electroless Nickel plated and often they look fine before cleaning in a multi-stage ultrasonic cleaner. However, after processing in the ultrasonic cleaner (two stages of ultrasonics, one rinse, one dry --cleaner is Blue Wave Detergent #25-I, 4 parts purified (Seattle city water through filters) deionized water to 1 part liquid detergent). Many of the parts come out with brownish to blackish spots of irregular shapes. They kind of look like the variation you would get with water spots. Strangely, if we don't turn on the ultrasonics, we don't have this staining issue (though we have to soak them longer to get fingerprints, etc. off of them). We are trying to get them clean for oxygen service. The brownish/blackish spots can be buffed off but that is labor intense and thins the surface.

Ed Huncovsky
- Kirkland, Washington
May 7, 2009

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Black patches on Nickel plated aluminium parts

Q. Hi,
We are facing black patches in High Phosphorous nickel plating on Aluminium parts.

We do plating twice, first time 25 to 30 micron electroless nickel, then Copper band soldering, then electrolytic nickel plating 3 to 5 microns.

What would be the root cause for this. Please help.

Santosh Musandi
Quality analyst - Bangalore, Karnataka, India
May 21, 2014

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Q. A medium phosphorous electroless nickel plated 17-4 PH stainless steel part on one of our handheld devices becomes tarnished very quickly. It is mainly a aesthetic problem but we would like to prevent this from happening.
Are there alternative finishes that look similar to electroless nickel that do not develop this problem or are there other options out there to prevent the electroless nickel finish to tarnish?

Dominik Scheffler
- Phoenix, Arizona, USA
January 18, 2017

Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)

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Ground electroless nickel plating is turning black

Q. Hello Sir/Madam,
I am from India. Past 2-1/2 years I am working in Electroless Nickel Plating Shop. Here we use PMD chemicals.

After Completion of Electroless Nickel Plating (40 - 45 µm) and heat treatment (400 °C at 1 hour), after cooling, I moved the finished job to Grinding section; they cut half of the plating from the job (20 - 22 µm). Then the job moved to Packing; they packed immediately and moved to the Customer. My customer uses this part at any time. Sometimes they store my job in stores and use after 5 or 6 months*.

I received a complaint from customer "your job is fully black and I cannot accept this lot". Actually my final job is Fully silver white colour. How did this Job Change into Black? Please Help and give some suggestions to avoid this problem in future.

Arul Murugan
Plating Company - Chennai, Tamil Nadu, India
March 30, 2017

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Ed. note: * -- Because this posting is about inadvertent blackening of electroless nickel, we moved it to this thread. Arul originally posted under the topic "Electroless nickel plating on cast iron parts", so we assume his parts are cast iron.

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EN Staining Issues Niklad 847 Mid-phos chemistry

August 16, 2017

Q. Hello all,

Before I get into asking questions, I would first like to thank Finishing.com for being the resource it has been to me thus far. As a 26 year old just getting my feet wet in the world of metal finishing, I have to say that you guys have been a huge help from day one. With just at 1 full year of experience, I am realizing quickly how much depth there is to metal finishing. With that being said, I would like to also mention that I've primarily been working with chromate conversion coatings (III and VI) as well as NDT (FPI/etch and MPI).

Although I've worked around EN almost everyday, supporting my shops platers with tank adds and titrations, etc., I find that questions I often have don't seem to be as easily answered as I would think. I've recently started learning how to plate aluminum components and have what I feel is a pretty good understanding of the pretreatment process -- zincating and what not -- but when it comes to the EN bath itself and troubleshooting issues, I am a little overwhelmed.

Trying to transfer "best practice" processing techniques that I picked up learning conversion coatings doesn't seem to always be "best practice" with EN (thorough and CLEAN rinsing, precise timing in baths for repeatability, accurate bath management, drying, etc. ), which leads to a question I have that is driving me crazy ...

Has anyone used MacDermid Enthone's Niklad 847 midphos EN? We were using the 807 Niklad before I started plating and recently switched. Of all the ideas I have had about my particular issue, the actual chemistry is the only thing I can think of that is potentially causing problems. The issue is the presence of light brown, to almost black staining on the surface of the freshly plated aluminum parts as they are coming out of the EN bath. I've tried everything I know how to do to alleviate this, but have had no luck and have not been able to find a solid answer as to why this is happening.

As far as technique is concerned, the bath is well under the maximum amount of metal turns so zincate contamination and other particulates are pretty much out of the question. We run the bath constantly through 2x 1-micron filter bags. The bath was made new today after the tank was passivated overnight. I flushed with RO water and made sure there was nothing in the tank whatsoever before preparing a fresh bath. When I plated the parts, the rate was consistent and timing was dead on for .0006" of thickness. I rinsed thoroughly with RO coming out of the bath, and went into a brand new RO dead rinse. Agitated the rack of parts manually, very vigorously. The rack is freshly coated. No bare areas or anything for solution from anywhere to be trapped. I hose rinsed out of the dead rinse (RO) and went into a fresh, heavily agitated RO counterflow rinse for a ridiculous 5 minutes. I hose rinsed with RO coming out of the counterflow and finished in a hot RO rinse (150 °F) before a quick air hosing and into a 170 °F dryer.

Sure enough the parts were stained. The parts themselves have threaded holes that I solvent cleaned and dried prior to masking with silicon plugs that fit quite snug. Bleedout from acid seems a little extreme to me. Especially since there are no bare areas or blisters around the plugs. The parts are only about 2 inches by inches, very light, threaded holes very small. It just doesn't seem likely that bleedout would occur in a way that would make this happen so consistently. I agitate parts in pretreatment rinses 3-5 minutes usually. I focus my hose rinsing on these areas as well. I feel like any small amount of potential bleedout should be mitigated by the cleaning and pH of the EN bath and the rinsing that follows it.

I can't even find the 847 solution on the Enthone website or internet period. I assure everyone this is definitely a MacDermid EN chemistry. DI water for rinsing is out of the question unfortunately. Does anyone have any insight or suggestions? Any advice would be much appreciated. Thanks!

Brandon Mascoe
Metal Finishing shop processing technician - Indianapolis

• Please see also thread 42907, "Black/Brown stains on electroless nickel plating"